//What’s the Difference Fasting and Eating Less? (Science of Fasting)

What’s the Difference Fasting and Eating Less? (Science of Fasting)

“Breakfast of champions.” What’s the difference between eating less food and eating no food? Well, Lets look at two different situations. In 1944, a study called the Minnesota Starvation Experiment was conducted and was designed to understand the effects of caloric restriction on the body in order to gain some knowledge that would help people starving in the aftermath of World War 2. Thirty-six healthy men with an average height of 178cm (about five foot ten) and average weight of kilograms (or 153 pounds) were selected. For three months, they ate a diet of 3200 calories per day. Then, for six months they ate only 1570 calories. However, caloric intake was adjusted to attempt to have the men lose kilograms per week, meaning some men got less than 1000 calories per day. The foods given were high in carbohydrates- things like potatoes, turnips, bread and macaroni. Meat and dairy products were rarely given. During the six months, the men experienced profound physical and psychological changes. Everyone complained that they were too cold. One subject talked about having to wear a sweater in July on a sunny day. The subject’s body temperature dropped to an average of degrees Fahrenheit (degrees Celsius).

Physical endurance dropped by half, and strength showed a 21 percent decrease. The men experienced a complete lack of interest in everything except for food, which they were obsessed with. They were plagued with constant and intense hunger. There were several cases of neurotic behavior like hoarding cookbooks and utensils. Two participants had to be cut from the experiment because they admitted to stealing and eating several raw turnips and taking scraps of food from garbage cans. At first, the participants were allowed to chew gum, until some of the men began chewing up to 40 packages a day.

Now compare all this to the case of, a Scottish man who in 1965 fasted for over 380 days straight. That is, he took in no food whatsoever -nothing but water, black coffee and straight tea for just over a year. He lost 276 pounds, going from from 456 pounds to 180. A case report published by the Dundee University Department of Medicine in 1973 said …the patient remained symptom-free, felt well and walked about normally, and Prolonged fasting in this patient had no ill-effects. There were no complaints of mind numbing hunger and he kept the weight off- for several years his weight stayed around 196 pounds. This of course is not a perfect comparison, with the case of Angus, there’s only one subject and his starting weight was drastically higher compared to those in the Minnesota Experiment.

However, it does illustrate some very interesting points about just how different of a physiological response you get from fasting (that is, eating nothing) compared to eating less, or caloric restriction. Dr. Jason Fung, a Toronto physician specializing in kidney disease, and author of the Obesity Code, says that compared to fasting, Caloric Reduction will result in: less weight loss, more lean mass loss (i.e. more muscle loss), and more hunger. Lets start by talking about hunger. In Upton Sinclairs 1911 books The Fasting Cure, he writes about fasting as a means to improve health. In describing his first couple attempts at fasting he writes I was very hungry for the first day-the unwholesome, ravening sort of hunger that all dyspeptics know. I had a little hunger the second morning and thereafter, to my great astonishment, no hunger whatever-no more interest in food than if I had ever known the taste of it. Sinclair recommends doing quite long fasts – around 12 days or so. In a section addressing concerns about fasting he writes Several people have asked me if it would not be better for them to eat very lightly instead of fasting, or to content themselves with fasts of two or three days at frequent intervals.

My reply to that is that I find it very much harder to do that, because all the trouble in the fast occurs during the first two or three days. It is during those days that you are hungry. Then he says: …perhaps, it might be a good thing to eat very lightly of fruit, instead of taking an absolute fast-the only trouble is that I cannot do it. Again and again I have tried, but always with the same result: the light meals are just enough to keep me ravenously hungry… In the book he says you will know when you should finish fasting, because your hunger will return. He quotes a letter he received from a 72-year-old man saying After fasting twenty-eight days I began to be hungry and broke my fast with a little grape juice, followed the next day with tomatoes, and later with vegetable soup.

He quotes several other letters he received from readers and this disappearance and reappearance of hunger is a common theme. Everyone who wrote to him fasted for at least 10 days, saying they only broke their fast when hunger returned. This phenomenon runs contrary to the idea one would get hungrier and hungrier as long as they dont eat. However, most people have experienced for themselves that this is not the case. Some will find that they are not hungry at all in the morning or at least they are not as hungry as they are for lunch or dinner.

But unless you are eating in your sleep, the morning is when you have gone the longest without food. Some of this can be explained by the hormone Ghrelin. Ghrelin, known as the hunger hormone has been found to increase appetite and weight gain. A study at the Medical University of Vienna looked at patients participating in a 33-hour fast. Their ghrelin levels were checked every 20 minutes. Heres how the levels changed over time. What’s interesting is ghrelin is lowest at 9:00AM, which is when they have gone the longest without eating. And, Ghrelin comes in waves and overall doesn’t rise during the period the subjects were fasting. Then, As you can see, ghrelin rises in sync with normal lunch and dinner times, as if the body had learned to expect food at that time. However, that ghrelin rise spontaneously decreases after 2 hours without food. I’ve experienced this kind of spontaneous decrease in hunger myself many times when I was working as a consultant.

Lunch time would come and I would be hungry, but I was too busy to eat so I just kept working. Pretty quickly I forgot about eating and wasn’t particularly hungry until dinner time. This is very helpful to keep in mind if you’re doing a long fast or even if you’re starting intermittent fasting – you’re going to get annoying waves of hunger, especially around the times that you usually eat. But, it won’t get worse, the hunger will simply go away if you are patient. Another study concerning ghrelin was done at Aarhus University Hospital in Denmark and it shows what happens if you do a longer fast. They looked at the ghrelin levels of 33 subjects who fasted for 84 hours. So, did they get increasingly hungrier throughout the fasting period? Well, No. Their ghrelin followed similar rhythms each day but actually decreased the longer they fasted.

Going longer without food actually made them less hungry. This gives credence to what Upton Sinclair and his readers said about hunger disappearing after the first 3 days of fasting. I’ve done a couple 5 and 6 day fasts in the past myself and this was indeed the case. Actually, I did a 4-day fast last week and again the 4th day was when I had the least hunger. Another thing that may be contributing to this phenomenon is that you are entering ketosis. Ketosis is a physiological state where your metabolism switches to using primarily fat for energy. For this reason ketosis is popular as a weight loss method, but it has many other benefits including better physical and mental efficiency. Ketosis occurs when you restrict carbohydrates down to 50 grams or less and you don’t eat too much protein. Everyones body is a bit different so you might have to eat even less carbohydrate or may have room for more, but the recommended ratio of a ketogenic diet is to get 5% of your calories from carbs, 25% from protein and 75% from good fat. A simpler way to enter ketosis is just don’t eat anything for a long enough time.

This is one of the major points in the difference between fasting and caloric restriction. The problem with the subjects in the Minnesota Starvation experiment was that they were eating just enough to keep them out ketosis and keep their metabolism primed for burning carbohydrate (glucose), so they couldn’t use their body fat for energy. This explains a lot of things like why they were losing their strength and were very sluggish and cold.

It also clears up why Upton Sinclair said fruit or light meals were just enough to keep him ravenously hungry and far weaker than if he had just eaten nothing. As I explained in my last video, insulin is necessary for glucose to get into the cell to be used for energy. When you eat carbohydrates, the pancreas secretes insulin to deal with it and too much insulin hampers the action of something called hormone sensitive lipase which is necessary to mobilize fat and use it for fuel. Though, keep in mind that grains or refined carbohydrates will provoke a much higher insulin response than say green vegetables.

Now because the body is having a hard time using its fat for fuel, it will do a couple things: One, it will simply slow down metabolism to preserve energy. In the Minnesota Starvation experiment, the subject’s metabolism dropped by 40 percent. Their bodies didn’t have access to its stored energy, and their restricted calorie diets don’t provide much fuel so there’s no choice but to slow down the metabolism.

Ironically, in the case of fasting, as Jason Fung points out – metabolism actually goes up. “If you don’t do anything about your insulin and just reduce your calories, your metabolism goes down. But what happens during fasting? Well, here’s a study of 4 consecutive days of fasting. What happens to your REE – this is this middle line here, that’s the resting energy expenditure. It doesn’t go down, it goes up. You’re burning more energy than you did.” The other thing the body will do when it can’t use fat for fuel is to break down muscle into glucose through a process called gluconeogenesis.

The body doesn’t want to do this too much because it’s not very smart to completely eat through something as important as muscle, but when it can’t access its own stored energy is more likely to resort to this. This is why you’ll experience more muscle loss on caloric restriction than if you ate nothing. When you are fasting, Human Growth Hormone is released. As the name implies, Human Growth Hormone is an anabolic hormone – a hormone conducive to growth. In Leninghers Principles of Biochemistry textbook they give the example of how injecting the human growth hormone gene into a mouse makes it unusually large. As explained in Guytons Textbook of Medical Physiology:”…growth hormone also mobilizes large quantities of free fatty acids from the adipose tissue, and these in turn are used to supply most of the energy for the body cells, thus acting as a potent “protein sparer.” “That is human growth hormone is protecting your muscles from breaking down.

The study I referred to earlier about subjects undergoing an 84 hour fast shows that growth hormone rises significantly after the second day of fasting. As mentioned earlier, you should enter ketosis sometime within the first 3 days or so of fasting, and it depends on how much you are moving around and what your diet was like before starting the fast. The state of ketosis is a great indicator that your body is making good use of its stored body fat for energy. In Tim Ferriss book Tools of Titans, Tim talks about his first clinically supervised 7 day fast. For some sort of liability reasons, he wasn’t allowed to exercise or leave the facility. Considering exercise is a potent stimulator of human growth hormone and will help deplete glucose stores, not getting any exercise is a great way to prevent yourself from getting into ketosis during a fast. Its also a great way to lose muscle.

Tim says he lost 12 pounds of muscle during the overly restrictive clinically supervised 7 day fast. But, when following a protocol designed to get him into ketosis as soon as possible – involving things like 4 hours of brisk walking, he did a ten day fast and apparently lost zero muscle mass. One last factor in Ketosis preserving muscle is leucine. When you’re in ketosis, you have a higher fasting blood leucine level. And leucine is a key branch chain amino acid that has an anabolic effect on the body so it preserves lean body mass. A lot of people interested in building muscle may be worried that fasting or a ketogenic diet wouldn’t work for them because insulin and therefore carbohydrates are necessary for protein synthesis (i.e. muscle growth), but actually this leucine fills that role and is a good trigger for protein synthesis. So, just to sum all this up: compared to a conventional calorie restricted diet, fasting means you lose more weight in the form of fat, you keep more muscle, you have more energy, and you are less hungry. If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low-calorie diet.


As found on Youtube